Synthesis of dibenzonaphthyridine derivatives containing cyanoacrylic acid

Synthetic organic dyes with or without metals are generally used as sensitizers in dye sensitized solar cells (DSSC). Organic dyes without metals are generally consist with a structure of donor-conjugated π bridge-acceptor (D−π−A) and carry out intramolecular electron transfer from donor (D) to acceptor (A) through the π bridge. Aromatic π bridge is the major component of these dyes which increases absorption capacity and provides intramolecular electron transfer. Fused aromatic π bridges exhibit broad and intense spectral absorption in the visible-light region, which is beneficial to enhance photovoltaic performance of these dyes. Molecular structures of dibenzonaftiridine compounds are also composed of fused aromatic rings. Although they are very important due to their various biological activities and photophysical properties, there are limited numbers of studies on the direct synthesis of these compounds. In this study, four compounds bearing metoxy, trimethoxy, dimethylamino, methyl groups as donors, dibenzo[b,h][1,6]naphthyridine as π bridge, cyanoacrylic acid as acceptorweresynthesizedforthefirst time. At the outset, the starting compound 2'-aminoacetophenone was brominated to provide a bromine source to the palladium-catalyzed cross-coupling reactions in the following steps.The obtained compound was converted to 6-bromo-4-chloroquinoline-3-carbaldehyde (TS2) by Vilsmeier reaction.This compound was reacted with various aniline derivatives to yield donor containing dibenzo[b,h][1,6]naphthyridine derivatives (TS31, TS32, TS33, TS34). Subsequently,these compounds containing bromine were converted to aldehyde group containing derivatives (TS41, TS42, TS43, TS44) by the Suzuki-Miyaura reaction.Finally, these aldehyde group-containing compounds were converted to dibenzo[b,h][1,6]naphthyridine compounds containing cyano acrylic acid (TS51, TS52, TS53, TS54) by Knoevenagel reaction usingcyanoaceticacid. As a result, dibenzo [b,h][1,6]naphthyridine compounds with D−π−A system were obtained for use in dye sensitized solar cells.The structures of the synthesized compounds were confirmed by taking 1H NMR, 13C NMR, HRMS-ESI (+) and IR spectra.